1. Field of the Invention
The present invention relates to a method and a device for sealing the mouth of a pouch made of a heat-fusible material.
2. Description of the Prior Art
Fusing with hot plates is the commonest way of sealing the mouth of a pouch packed with an article, if the pouch is made of a heat-fusible material such as synthetic resin. But this method has a drawback that if the packed material is powdery or fatty, it tends to adhere to the inner surface of the pouch at its mouth, resulting in poor fusing.
Japanese Unexamined Utility Model Publication No. 58-156606 tackled this problem by use of ultrasonics. The heat-sealer disclosed in this Publication imparts ultrasonic vibrations to the mouth of a pouch to induce molecular-level vibrations. The mouth is fused together by heat generated by the molecular-level vibrations. With this method, a perfect seal is obtained even if a powdery or fatty material is adhering to the inner surface of the mouth. In order to efficiently impart vibrations to the sealing portion to ensure a strong bond, the sealing portion has to be tightly pressed between the vibrator and its support member while being vibrated. But since the pouch to be sealed is usually made of a limp film, it is difficult to insert it into between them.
In the above-described Japan 58-15606 the support member is in the form of a roller having its periphery toothed. With the rotation of the roller, its toothed surface catches the mouth of a pouch to feed it into the sealing station. But in this method, the mouth is fused only intermittently according to the distances between the teeth. Thus this method is not applicable to a pouch containing a powdery or liquid material because such a material tends to leak through openings between the fused portions. If the roller surface is formed with so fine teeth that the openings formed between the fused portions will be small enough to prevent the content from leaking, then it becomes difficult for the roller to smoothly catch the pouch and draw it into the sealing station.
On the other hand, Japanese Unexamined Patent Publication No. 52-146387 discloses a device for sealing a carton made of cardboard by vibration heating. With this device, the carton to be sealed is fed into a sealing station intermittently. A vibrator is lowered to be pressed against the carton after the feed of carton has been stopped. Though with this device, the problem with the first-mentioned Publication has been solved, it is necessary to drive belt conveyors intermittently. This will complicate the control of the machine and worsen the working efficiency.